Cited as a means for obtaining a radiographic image for medical diagnosis or non-destructive testing of a various types of tissues and applying it to diagnosis and radiographic flaw detection are: radiography by a combination of a silver halide photographic light sensitive material and a radiographic intensifying screen, or radiographic image conversion method by the use of a fluorescent substance from which, after absorption of radiation energy, the accumulated radiation energy is emitted in the form of fluorescence by stimulation with electromagnetic waves such as visible light or infra-red rays (hereinafter referred to as photo-stimulative fluorescent substance).
Diagnosis or examination with radiography is such that radiation transmitted through or emitted from photographic object is converted, through absorption by fluorescent substance contained in the radiographic intensifying screen and its excitation, into visible light, which produces a radiographic image on the silver halide photographic light sensitive material. The radiographic image is formed by exposing, to radiation through an object, the silver halide photographic light sensitive material having on one side or both sides of a support a silver halide emulsion layer, which is in contact with a radiographic intensifying screen to a radiation through an object.
The fluorescent substance has a high emission luminance and can form a radiographic image with a relatively small dose of radiation, so that exposure to radiation of the object can be minimized. It is well known that sharpness and graininess of the image depend upon the particle size and dispersion of the fluorescent substance, and homogeneity in a fluorescent substance containing layer.
The radiographic image conversion method employing the photo-stimulative fluorescent substance includes the employment of a radiographic image converting panel containing the photo-stimulative fluorescent substance (hereinafter, referred to as photo-stimulative fluorescent substance panel). In this case, the radiation transmitted through or emitted from the object is absorbed by a fluorescent substance contained in the panel, followed by stimulating time-sequentially the fluorescent substance with electromagnetic waves such as visible light and infra-red rays (also known as stimulating light), and emitting the radiation energy accumulated in the fluorescent substance, in the form of light (photo-stimulated luminescence). The photo-stimulated luminescence is read as electric signals and based the electric signals obtained, the object or its radiographic image is reproduced as a visible image. The panel which has already been read is treated to eliminate residual images and made ready for the next photograph. Thus, the conversion panel can be repeatedly employed.
The radiographic image converting panel is also dependent upon the particle size and dispersibility of the fluorescent substance, and homogeneity in the fluorescent substance containing layer.
It has been regarded that since the fluorescent substance size is as large as 1 to 30 .mu.m of particles and is readily dispersible, the fluorescent substance can be dispersed in any resin to some extent. Accordingly, few studies thereof have been made as to the resins for use in dispersing the fluorescent substance,. For example, a technique for improving the dispersibility by using a mixture of three kinds of resins is disclosed in JP-A 61-277098 (herein the expression, "JP-A" means unexamined and published Japanese Patent Application. However, it was proved that this technique did not contribute to enhancement of dispersing capability of the resin with respect to the fluorescent substance and had little effect in homogeneous dispersion.
Inventors of the present invention have made studies of dispersibility of the fluorescent substance. As a result, it was found that sharpness and graininess were markedly improved by enhancement of dispersing capability of the resin for the fluorescent substance.